1. Field of the Invention
The invention concerns a stator structural unit for an electrical machine, particularly an alternating-current machine [a. c. generator] in the form of a transverse-flux machine.
2. Description of the Prior Art
Electrical machines in the form of a. c. generators, particularly transverse-flux machines, are known in various embodiments from a multiple number of publications. In this connection, refer to the publications:
1. DE 3,536,538 A1
2. DE 3,705,089 C1
3. DE 3,904,516 C1
4. DE 4,125,779 C1
These essentially describe the basic principle and the construction of a. c. generators operating according to the transverse-flux principle. The machines comprise at least one stator structural unit with one stator, particularly comprising a multiple number of strip-wound cut cores, with at least one armature winding and a rotor with magnetic excitation arranged lying opposite the winding. The known stator structural units thus have a stator housing with cross-pieces and with so-called digits for fixation and heat discharge at the strip-wound cut cores of the outer and inner stators, as well as a support for the centering of the armature winding. The outer strip-wound cut cores, i.e., those strip-wound cut cores of the outer stator, are fixed in the radial direction between the cross-pieces by means of adjusting screws and retaining clips, or, in other known designs, are fixed roughly radially by means of a retaining ring of nonconducting material. The strip-wound cut cores of the inner stator are roughly radially fixed between the digits of the stator housing in the peripheral direction and through the coil. For final fixation, the stator which has been premounted with a suitable casting compound and with the use of a so-called core ring, is cast. The casting of the stator unit is a very time-consuming process, due to the very complicated housing structure. So-called winding and impregnating devices are necessary for production of exciting coils. Due to the multiple number of individual parts and their complex configuration, assembly is very time-consuming, particularly of the strip-wound cut cores at the outer stator with fastening clips. By analogy, this holds true also for the strip-wound cut cores contained in the inner stator. Another essential disadvantage in the production of the stator structural unit comprises the fact that the exciting coil and the strip-wound cut cores must be cast in the stator housing, and a post-processing of the casting compound is usually always necessary. The casting compound in turn limits the admissible maximum temperature of the entire structural unit to a specific value during operation. This in turn acts negatively on the obtainable permissible continuous output. Production itself requires expensive configured tools as well as highly qualified employees for assembling.
Therefore the object of the invention is to further develop a stator structural unit of the type named initially for an a. c. generator, particularly a transverse-flux machine, such that the named disadvantages are avoided. Taken individually, the stator structural unit will have a simple structural design, which assures a cost-favorable production and easy assembly. An adverse effect on the properties with respect to heat discharge is to be avoided.
It is provided according to the invention to design stator structural units for electrical machines, particularly transverse-flux machines, with at least one stator unit bearing an armature winding, which forms an air gap with a rotor in the installed position, considered in the radial direction in axial section, of at least one electrical ground element configured preferably in annular form extending annularly in the peripheral direction considered in the installed position and tooth elements which can form a structural unit with the ground element. The annular electrical ground element is produced by powder metallurgy or manufactured from a component that has been produced by powder metallurgy. The tooth elements are comprised of a soft magnetic material or substance. The tooth elements can thus be coupled with the annular ground element such that the tooth elements, considered in an axial section of the electrical machine, and together with the annular ground element, describe an essentially U-shaped cross-sectional surface, whereby the two legs of the U-shaped section are each formed of tooth elements. Tooth elements in the installed position are to be understood as projections extending to the rotor, which form edges or edge surfaces in the peripheral direction, whereby the two edges pointing together in the peripheral direction describe two stator tooth gaps in the peripheral direction of adjacent tooth elements.
A plurality of tooth elements, which lie on a common diameter with respect to the axis of symmetry of the electrical machine, in the axial direction and considered in axial section, or which can be described by projecting onto the axis of symmetry through a common point on the latter, form a so-called soft-iron unit. In order to produce a U-shaped cross section, the ground element is coupled with two soft-iron units.
Preferably star-shaped soft-iron elements are designed in the peripheral direction such that they have a multiple number of individual projections extending away from the annular ground element in the direction of the rotor and describing the tooth elements. The soft-iron units describing the tooth elements in the peripheral direction are arranged at specific distances from one another, depending on the configuration of the rotor. Preferably, the projections forming the tooth elements are combined with the annular ground element, particularly joined in a radial manner, by means of a common base unit extending in the peripheral direction, with which the latter preferably form a structural unit.
The tooth elements or the soft-iron units formed from these elements, particularly two tooth elements each time, form the U legs of the stator unit extending away from the annular ground element each time, viewed in an axial section. The tooth elements of a soft-iron unit can thus be coupled each time individually in a frictional connection and/or form-fitting manner with the electrical ground element. Preferably, however, the soft-iron units are designed each time as annular elements or the individual tooth elements are carried by a common base unit. In order to avoid circular currents, the annular elements are designed so that they are interrupted in the peripheral direction, at least at one place. The subdividing into a multiple number of segments, whereby each segment contains a multiple number of tooth elements, is also conceivable. The coupling or combining of the soft-iron units with the annular electrical ground element can be designed in different ways. Connections are thus conceivable by means of:
a) frictional connection
b) form-fitting connection
c) frictional and form-fitting connection.
In designs with frictional connection, preferably the soft-iron units are assembled with the annular ground element by means of a press connection. This offers the advantage that there is no dependence of service life on the composite materials used, since there is no pure material connection. The concrete configuration of the press connection can be produced in different ways. Selection can be made according to the opinion of the competent person skilled in the art.
The basic possibility for the configuration of elements of electrical machines from or as powder-metallurgically produced parts is already known from the publication xe2x80x9cComposites pave the way to the electrical machine designs of the futurexe2x80x9d (Hxc3x6ganxc3xa4s Iron Powder Information PM 95-4). These involve, however, the complete design of elements from such materials. The inventors have recognized the fact that the gross transfer of this possibility to transverse-flux machines does not offer the desired advantages and thus searched for more suitable designs producing improved results.
The electrical ground element extending in an annular manner in the peripheral direction, considered in the peripheral direction, can be designed as
a) one part or
b) several parts.
In the design according to variant b), the annular contour is fixed by attaching the element parts of the ground element to the housing in the peripheral direction.
The stator unit bearing the winding of the ground element and soft-iron units or tooth elements can be offered as a compact and already pre-assembled basic structural unit and can be integrated into the stator structural unit, particularly the stator housing. The number of structural elements to be fixed opposite one another in the axial and radial directions is relatively small, and fixation is done on the basis of the design of the stator structural unit. The armature winding is arranged between the soft-iron units. The entire unit including the armature winding can be impregnated with an insulating agent, for example, an insulating resin. The part of the stator unit comprised of material produced by powder metallurgy offers the advantage of isotropic, magnetic and electrical properties. Depending on the stator construction, this region is only necessary as the ground region for the magnetic flux between the soft-iron units or the tooth elements forming these units. The poorer permeability in this region, which is caused by the material properties, is acceptable, due to the enlarged flow cross-section opposite the tooth elements.
The use of the annular ground element in the described manner offers the advantage of creating a compact stator component with improved strength, which can be easily manufactured, and has optimal electrical and magnetic properties.
In a preferred embodiment, the soft-iron units or the tooth elements forming these units are a bundle of laminations layered in the axial direction, which comprise annular elements of correspondingly stamped-out sheet metal layered one behind the other, considered in the axial section in the installed position. Considered in the peripheral direction, each individual annular sheet metal element and thus each bundle of laminations has open-edge recesses in the region of the peripheral surface aligned to the rotor, for the formation of the projections describing the tooth elements. These open-edge recesses are arranged distributed over the periphery of each individual annularly shaped sheet-metal element and thus also the bundle of laminations at uniform distances. The annular configured sheet-metal elements and thus each bundle of laminations describes an essentially star-shaped contour considered in the installed position in the peripheral direction. The number of annular individual sheet-metal elements layered on top of one another or arranged behind one another in the axial direction in the installed position depends on the design of the entire electrical machine. The representation of the soft-iron elements as a bundle of laminations assures a good permeability in the tooth region and minimizes the eddy current losses that occur.
Preferably, in the case of transverse-flux machines, the stator unit bearing the armature winding, particularly the stator part, is formed by an inner stator of a transverse-flux machine. This offers the advantage of screwing into the stator housing the inner stator, or at least the stator unit assigned to one pole structure of the rotor, as a completely pre-assembled structural group comprised of the annular ground element and the tooth elements forming the soft-iron units. In the case of a symmetrically constructed transverse-flux machine, the rotor generally has two pole structures, each extending away from a central carrier disk and the pole structures each belong to one electrical phase. Accordingly, the corresponding stator unit can also be assigned to each pole structure. The total structural unit of the stator in this case is comprised of at least two stator units configured according to the invention, which function as an inner stator and are assigned to the rotor, particularly to [each of] the pole structures on both sides of the carrier disk. The connection between stator housing and inner stator thus is made in the region of the annular ground element, since this can be produced simply without great expenditure in this region. However, configurations of transverse-flux machines with two stator units bearing an armature winding, which can be assigned in the radial direction on both sides of one pole structure and in which the outer stator is prefabricated also as a pre-assembled structural unit in the described manner, are also conceivable. Another, third possibility consists of designing only the outer stator as the component bearing the armature winding.
In the case of symmetrical constructed transverse-flux machines with a rotor with two pole structures, at least
a) two stator units configured according to the invention are provided as the total structural unit [of the] inner stator, and/or
b) two stator units configured according to the invention are provided as the total structural unit [of the] outer stator,
each of which form an air gap with the rotor in the radial direction and are integrated in the stator housing or are fastened to it.
In designing a transverse-flux machine with at least one stator unit bearing the armature winding in the form of the inner stator, preferably the outer stator is designed of a multiple number of individual stator elements, which are comprised of materials produced by powder metallurgy and compacted, as a solid-profile structural part, which [elements] can be attached directly to the stator housing with simple fastening elements. Preferably, attachment is made by means of screw elements. In order to be able to use solid parts that are configured as simply as possible and that are easy to assemble, which can be used as a standard type in different machine designs, these have an essentially planar-shaped stop surface in the region of their contact surface with the inner surface of housing 5. Correspondingly, the front surface of the housing turned toward the rotor in the installed position also is preferably designed with planar stop surfaces running in the axial direction. To guide the connection elements, passage openings are provided on housing 5, which can be furnished with a thread and threads can be provided in the stator elements.
The configuration of a stator unit bearing the armature winding according to the invention offers considerable functional advantages in addition to a number of cost and manufacturing advantages. In particular, an improved heat discharge into the water-cooled stator housing can be made possible by the configuration of the inner stator element designed in combination with the simplified configuration of the outer stator. As a consequence of the frictional connection, which makes possible avoiding the use of casting compounds for radial and axial fixation of the stator unit, in particular, the armature winding can be cooled directly, for example, by cooling with the oil mist produced by means of rotor rotation. In addition, an increase in the admissible continuous output by approximately 25% is to be expected by avoiding casting compounds, since the admissible maximum temperature during operation is no longer limited by the casting compound.
The stator housing itself can be constructed in a very simple manner; in particular, slots are no longer necessary for taking up strip-wound cut cores. Winding and impregnating devices for producing the armature coil as well as the means for binding the components are no longer necessary. The previously time-consuming assembly of the outer strip-wound cut cores with fastening clips is reduced to simple screwing in of powder [metallurgy] elements comprising soft magnetic material. The stator unit configured according to the invention, independent of whether it is designed as an outer or inner stator, can be supplied as a pre-assembled, prefabricated structural unit. A casting of the armature coil and the strip-wound cut cores in the stator, which was necessary earlier, can be dispensed with, whereby the necessary subsequent post-processing will also be avoided. In addition, no complicated tools and no special know-how of the employees that are entrusted with it are necessary for producing the individual elements and for assembling these.